There are a limited number of antennas that can receive multiple polarizations and frequencies simultaneously. For example, the DirecTV Slimline 3 Dish reflector antenna receives multiple polarizations and frequencies simultaneously. In this product, there are 2 Ka-band receivers and 1 Ku-band receiver operating simultaneously from the same reflector. This is accomplished by placing multiple feeds at different locations along the focal axis of the reflector. In this case, based on the pointing of the dish and the positioning of the 3 receivers, simultaneous reception from 3 satellites (99°, 101°, 103°) is achieved, with the Ka-band satellites providing 2 circularly polarized signals simultaneously. The DirectTV Slimline 5 Dish reflector antenna sees 5 satellites simultaneously—99°, 101°, 103°, 110°119°. (99,103° is the Ka-band). The operations of these products are limited to receive.
Two limitations of such dish-based antennas are that a dish needs to be pointed towards the satellite and that the angular difference between the look angles of 2 or more feeds within 1 reflector is limited to approximately 10 degrees, e.g., Slimline 5 (99°-119°). This is dependent heavily on the shape of a dish, which can be engineered to various specifications. However, all dishes rely on a focusing behavior to achieve directivity, and thus the more focusing needed to close the link, the less angular coverage is achievable for a reflector dish having a constant area.
Another commonly used approach to achieve dual frequency simultaneous performance is dual-band arrays comprised of radiating elements having 2 operating bands. These are often realized using resonant patches or similar shapes such as ring resonators. One recent example is described in U.S. Pat. No. 8,749,446, entitled “Wide-band linked-ring Antenna Element for Phase Arrays,” issued Jun. 10, 2014. This implementation allows neighboring commercial and military Ka receive bands to be covered simultaneously, which are 17.7-20.2 GHz for commercial and 20.2-21.2 for military. However, there is no ability to point at more than 1 source simultaneously. Furthermore, there is no system level allowance described giving sufficient isolation to support simultaneous transmit and receive operation.
Thus, typically, with dishes that must simultaneously point in largely different directions (more than an estimated 10 degrees difference), that must track earth orbiting satellites (O3b installation with two gimbaled dishes), or communicate across largely different frequency bands, two completely separate antennae and systems are required. This increases size, cost, weight and power.